An experiment has shown that bioimpedance analysis (BIA) was able to detect changes in total body resistance when different electrolyte solutions were infused. The changes in resistance were related to changes in osmolarity and electro-ionic state, not to volume of water infused. Therefore, BIA measures principally the electro-ionic state. Thus a measurement of fluid volume can be indirectly obtained from BIA. However, in the non-steady state such as acute fluid volume expansion, the measurement of water volume cannot be performed accurately.